Combine all ingredients, except popcorn, in a heavy saucepan. Bring to a boil; lower heat and cook to 250 degrees Fahrenheit on a candy thermometer. Mixture will bubble up in pan, so watch to keep from boiling over. Pour slowly onto hot popcorn and mix until well-coated. Let stand 5 minutes or until mixture can easily be formed into balls. Butter hands and form into 3-inch balls.